Question

Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. Find her
speed of rowing in still water and the speed of the current.​

Answer 1

Answer:

speed of rowing in still water: 6 km/hr and the speed of the current: 4 km/hr.

Answer 2

Answer:

Complete step-by-step answer:

Let us assume, the speed of Ritu rowing in still water is x km/hr.

Also we make the assumption that the speed of current is y km/hr.

We know that during upstream, the speed of Ritu rowing in still water and speed of the current of the river will be in opposite directions.

Hence the net speed at upstream will be =x−y km/hr

Similarly, during downstream, the speed of Ritu rowing in still water and speed of the current of the river will be in the same directions.

Hence the net speed at downstream will be =x+y km/hr

Now we need to use the given data in order to form equations in the assumed variables.

We know that,

Speed = distance/time

Also, it is given that Ritu can row downstream 20 km in 2 hours.

⇒x+y=202=10⇒x+y=10 ---- (1)

Similarly, it is given that Ritu can row upstream 4 km in 2 hours.

⇒x−y=4/2=2⇒x−y=2 ---- (2)

Now we need to solve equations (1)and (2).

Adding (1) AND (2),we get

x+y+x−y=12⇒2x=12⇒x=6 km/hr

Subtracting (1) AND (2),we get

x+y−x+y=8⇒2y=8⇒y=4 km/hr

Therefore, the speed of Ritu in still water is 6 km/hr and the speed of the current is 4 km/hr.

Hence option (D). Speed of rowing in still water: 6 km/hr and the speed of the current: 4 km/hr is the correct answer.